Herpes simplex virus (HSV) is the virus most commonly detected in diagnostic laboratories, accounting for over 40% of the viruses that were detected in cell cultures over a 25-year period. HSV causes a variety of clinical syndromes, and anatomical sites infected include the skin, lips, oral cavity, eyes, genital tract, and central nervous system. Generalized or disseminated HSV infection may occur in patients immunologically compromised by neoplasia, organ transplantation, inherited immunodeficiency disease, or AIDS, or through neonatal infection acquired by transmission of the virus through an infected birth canal. Most disseminated disease is fatal.